1. Field of the Invention
The present invention relates to a deposition process for a semiconductor device. More particularly, the present invention relates to a method for depositing thin film using plasma enhanced chemical vapor deposition.
2. Description of Related Art
Currently, chemical vapor deposition is the most important process in semiconductor manufacturing for depositing a thin film. In any semiconductor device where a thin film is required, whether the thin film is conductive, semi-conductive or dielectrics, the thin film is formed by chemical vapor deposition. Chemical vapor deposition is defined as the formation of a thin film by the reaction of vapor-phase chemicals that contain the required constituents. Thus, the thin film formed by such a method is superior in crystallinity, stoichiometry and other relevant material properties.
To lower the required reaction temperature so as to reduce the thermal budget of the process, plasma enhanced chemical vapor deposition gradually becomes one of the major thin film deposition processes. Normally, in a PECVD chamber, the deposition of a thin film on a substrate includes performing the plasma enhanced chemical vapor deposition process, followed by cleaning the substrate-free chamber. A pre-deposition process is further performed to isolate contaminants generated in the cleaning of the substrate-free chamber. A next deposition process is then performed.
However, as the thin film that is being deposited on the substrate is an insulating material layer or a high resistance thin film, such as, intrinsic amorphous silicon, a large quantity of charges is accumulated on the surface of the electrode in the PECVD chamber. If thin film deposition is continued for another batch of substrate, the distribution of plasma is affected by the uneven distribution of the accumulated charges, leading to a non-uniform thickness of the depositing thin film.